More than 1.5 million lives were spared thanks to a nationwide decrease in cancer deaths in the past 20 years, according to a new report by the American Cancer Society.

The report out this week reveals cancer deaths have dropped 22 percent since 1991. If they hadn't and had continued climbing -- as they had between 1940 and 1991 -- an additional 1,071,600 men and 447,700 women would have died, according to the report.

The American Cancer Society attributes the decline in the cancer death rate to a decrease in smoking, as well as "advances in cancer prevention, early detection and treatment."

"We can actually say that one and a half million Americans did not die because of that cumulative effort," said Dr. Otis Brawley, chief medical officer of the American Cancer Society.

And the elimination of smoking and issues related to obesity, high caloric intake and too little exercise could decrease cancer rates by an additional 40 percent in the next 20 years, he said.

Brawley said most of the prevented cancer deaths in the past two decades -- about 800,000 of them -- were prevented because people quit smoking or never started in the first place. One-third of all cancer deaths are the result of tobacco, he said.

And because more men smoked than women to begin with, that smoking has become less common across the board has resulted in more prevented cancer deaths among men.

Some states saw more improvement than others, with those in the Northeast seeing the biggest decline in cancer deaths and those in the South seeing the smallest, according to the report. Washington, D.C., saw a 33 percent decline in cancer deaths, and Oklahoma saw a 9 percent drop.

But the battle against cancer is far from over. The American Cancer Society estimates 1,658,370 new cases of cancer and 589,430 deaths from cancer next year. That means about 1,600 people will die each day in 2015.

Dr. Michael Neuss, chief medical officer at Vanderbilt-Ingram Cancer Center in Nashville, Tennessee, said the American Cancer Society's findings are good news, but there's more work to be done. There’s a need to continue to improve cancer prevention, detection and treatment and get those improvements to underserved populations, he said.

"That impact, though very impressive, still isn't enough," Neuss said. "We have a long way to go, but we're glad to have made these first steps."